1. Field of the Invention
The present invention relates generally to a resistor having a structure capable of preventing the variation in the resistance characteristics, improving the environmental resistance to humidity or the like, and further increasing the capacity of power and the mechanical strength, and more particularly, to a resistor having a structure in which at least one resistance film is embedded in a ceramic sintered body.
2. Description of the Prior Art
Conventionally, a cermet resistor mainly composed of a ruthenium oxide or a ruthenium compound has been widely used as a resistance element superior in precision. In fabricating such a resistor, a resistive paste composed of the above described ruthenium oxide or the like is printed on the surface of, for example, an alumina substrate to form a thick resistance film, and the resistance film is baked at temperatures of 800.degree. to 900.degree. C. A glass paste is applied to the surface of the resistance film on the alumina substrate and then, is baked to form a glass film. The glass film increases the environmental resistance to humidity or the like.
In the above described conventional resistor, however, the resistance film is directly coated with the glass film, so that the resistance value is liable to change and the characteristics are liable to vary. In addition, a pinhole may, in some cases, be formed in the glass film. In such a case, water or the like enters the resistor from the pinhole in an atmosphere of high humidity, to degrade the resistance characteristics. Furthermore, in the above described conventional resistor, the alumina substrate, the resistance film and the glass film differ in the coefficient of thermal expansion, so that the adhesive properties of the resistance film to the substrate are low. As a result, a large capacity of power is not obtained. The limit of the capacity of power is approximately 100 mW.